MISCELLANEOUS PAKASITIC AXD SAPKOPHYTIC ORGANISMS. 21 



eases occur locally and do not affect the leaves so seriously as to 

 cause them to fall before they should naturally. Collecting and 

 burning the fallen leaves and spraying where practicable will con- 

 trol this trouble. 



LEAF-BLISTER FUNGI. 



The leaf-blister fungi, belonging to the Exoaseese, attack the leaves 

 of a number of the deciduous trees and deform them. The species 

 which is best known in this country is probably Taphrina caerulescens 

 (Mont. & Desm.) Tul., which occurs upon the foliage of a number 

 of different species of oak in various parts of the country (114). 

 This disease attacks the newly formed leaves and causes an abnormal 

 growth, so that the leaf looks as if blistered over the affected areas. 

 The development of the fungus is quite rapid, and in extreme cases 

 defoliation may result from its attacks. The cumulative effect of 

 this disease where it occurs for several years upon the same trees 

 may result in the death of the affected trees. Burning the fallen 

 leaves and spraying where practicable will hold this disease in check. 



XECTRIA CIXXABARIXA. 



Nectria cimmbarina (Tode) Fr. has sometimes been considered a 

 parasite (23, 27, 52, 69, 102), but should really be considered a hemi- 

 parasite. Its spores obtain entrance into branch wounds caused by 

 hail, rodents, or birds, and the resulting mycelium grows through 

 the partially weakened wood and ultimately produces small red 

 clusters of fruiting bodies. The stimulus exerted upon some of 

 the living portions of the cambium layer by the presence of the 

 fungus mycelium frequently accelerates the callus production at 

 the edge of the wood. The callus of the first year is then invaded 

 by the fungous mycelium and killed, and a second layer of callus 

 starts to develop. This may happen for a number of years, until 

 a large area of dead wood having the appearance of a virulent canker 

 is formed on the branch or trunk. "Where these cankers grow to be 

 of any size they ultimately result in the death of the branch, or 

 where they occur on a young tree, in the death of the tree itself. 



There is a large group of the fungi belonging to the Pyrenomycetes, 

 a number of which attack the living tissues of the bark and the wood 

 of trees weakened by one cause or another. These fungi will usually 

 not attack a vigorous tree, but after a tree has been weakened, either 

 by unfavorable soil or atmospheric conditions or by the attack of 

 some animal, fungus, or insect, they gain a foothold and may pro- 

 duce more or less serious forms of disease. They likewise obtain 

 entrance through wounds into tissues which may properly be 

 called living tissues. The members of the genus Nummularis are 



149 



